Working Symbols

I have started again on my book. New ideas are coming to me each day, and though this is a good thing, it makes the book as a whole difficult to focus on, because most of my new ideas change the way everything is set up. I have enjoyed developing characters, but I can't tell if I'm shaping them into what they need to be or if they are shaping themselves based on the characteristics that I have given them. Sounds philosophical, doesn't it?